Effect of ionic liquid on the native and denatured state of a protein covalently attached to a probe: Solvation dynamics study

Abstract

Effect of a room temperature ionic liquid (RTIL, [pmim][Br]) on the solvation dynamics of a probe covalently attached to a protein (human serum albumin (HSA)) has been studied using femtosecond up-conversion. For this study, a solvation probe, 7-diethylamino-3-(4-maleimidophenyl)-4-methylcoumarin (CPM) has been covalently attached to the lone cysteine group (cys-34) of the protein HSA. Addition of 1.5 M RTIL or 6 M GdnHCl causes a red shift of the emission maxima of CPM bound to HSA by 3 nm and 12 nm, respectively. The average solvation time 〈τ(s)〉 decreases from 650 ps (in native HSA) to 260 ps (~2.5 times) in the presence of 1.5 M RTIL and to 60 ps (~11 times) in the presence of 6 M GdnHCl. This is ascribed to unfolding of the protein by RTIL or GdnHCl and therefore making the probe CPM more exposed. When 1.5 M RTIL is added to the protein denatured by 6 M GdnHCl in advance, a further ~5 nm red shift along with further ~2 fold faster solvent relaxation (<τ> ~30 ps) is observed. Our previous fluorescence correlation spectroscopy study [D. K. Sasmal, T. Mondal, S. Sen Mojumdar, A. Choudhury, R. Banerjee, and K. Bhattacharyya, J. Phys. Chem. B 115, 13075 (2011)] suggests that addition of RTIL to the protein denatured by 6 M GdnHCl causes a reduction in hydrodynamic radius (r(h)). It is demonstrated that in the presence of RTIL and GdnHCl, though the protein is structurally more compact, the local environment of CPM is very different from that in the native state.

Enhanced stability of the model mini‐protein in amino acid ionic liquids and their aqueous solutions

“…The precise behavior depends on the particular amino acid residue in the protein, its charge and electrostatic charge. This observation is in concordance with previous reports . Being coordinated by the ions, the mini‐protein exhibits hindered mobility, as indicated by the RMSD analysis in all six AAIL containing systems.…”

“…An extensive evidence exists that solvation plays a critical role in stability and function of most proteins . Accurate spatial information about proteins is obtained from routine diffraction experiments.…”

“…Phase transition can be hypothesized in this case. Bhattacharyya and coworkers used femtosecond up‐conversion to study solvation dynamics of a probe covalently attached via the lone cysteine group to a protein, in the presence of methylimidazolium RTIL. The average solvation time decreased from 650 to 260 ps, as 1.5 RTIL was supplied.…”

Interaction of proteins with ionic liquid, alcohol and DMSO and in situ generation of gold nano-clusters in a cell

“…Thus, the decrease in the r H is partly due to domain closure of the protein and partly due to dehydration. We now discuss an interesting case where an ionic liquid by itself causes unfolding of a protein, human serum albumin (HSA), while it causes refolding of the protein if it is unfolded beforehand by a denaturing agent, such as GdnHCl (Chowdhury et al 2012;Sasmal et al 2011b). In this study, the single cysteine residue (cys-34) of HSA is site specifically covalently labeled by the fluorophore 7-dimethylamino-3-(4maleimidophenyl)-4-methylcoumarin (CPM) (Fig.…”

Direct observation of the growth and shrinkage of microtubules by single molecule Förster resonance energy transfer

“…1/6 For the present system of donor (EGFP) and acceptor (alexa-568), R 0 in a protein F 0 F 1 -ATP synthase is reported to be 49 Å. 7 This cannot explain the observed fluctuations in B220 ms (0.22 s) time scale. 4 shows the fluctuation in e FRET and R DA in real time.…”